Internal combustion engines



APTii 1968 A. E. w. AUSTEN 3,377,925

INTERNAL COMBUST ION ENG INES Filed Dec. 6, 1965 United States Patent ABSTRACT OF THE DISCLOSURE A fr'ameless crankcase for an engine in which interconnected end and side walls of a lightweight material, such as aluminum or magnesium, constitute the outer surfaces of the crankcase and the walls have .a dynamic magnification factor of not more than three. Also, a variation in thickness along anyone wall should not be greater than 13:1 and a variation in thickness between any two walls should not be greater than 1.5 :1.

This invention relates to internal combustion'engines of the reciprocating piston type and in which the crankcase comprises a pair of end walls which respectively form supports for bearings for the crankshaft of the engine and a pair of side walls interconnecting and formed integrally with the end walls.

With such engines a great deal of noise is emitted from the aforesaid walls when the engine is in use and the object of the invention is to provide an engine of this kind in which the emission of noise from the walls is reduced as compared with known engines.

According to the invention an engine of the kind specified is characterized by the fact that the walls are not locally thickened and are of approximately equal thickness such that the dynamic magnification factor of each wall is not more than 3.

In the accompanying drawings:

FIGURE 1 is a part-sectional side elevation of one example of an engine in accordance with the invention, and

FIGURE 2 is a section on the line 2--2 of FIGURE 1 with parts removed for the sake of clarity.

Referring to the drawings there is provided an engine crankcase having a pair of end walls incorporating apertures accommodating bearing 10a, and a pair of side walls 11 interconnecting the end walls 10. Mounted within the bearings 10a is a crankshaft 12 upon which are mounted connecting rods 13 which are connected to pistons (not shown) accommodated within cylinder liners 14 mounted in the upper portion of the crankcase. Moreover, secured to the upper face of the crankcase is a cylinder head 15 in which are defined combustion chambers and in which is mounted the valve gear of the engine. The crankshaft 12 is also supported intermediate its length by an intermediate wall 16. In the particular engine shown the end walls, side Walls and intermediate wall extend well below the axis of rotation of the crankshaft but this is not essential to the present invention.

As shown, the end walls, side walls and the corner portions are of equal thickness and no strengthening ribs are provided as is the case with known crankcases. In view of this the thickness of the walls is required to be such that the loads imposed upon them when the engine is running can be safely carried by the walls. It will be appreciated that accessories such for instance as a fuel pump have to be mounted on the engine in a position to be driven by the crankshaft and for this purpose a mounting boss or bosses must be provided. Such a boss is indicated at 17 in FIGURE 1. Moreover, it is necessary to provide supports for the liners 14 and to define passages 3,377,925 Patented Apr. 16, 1968 within the block for the passage of cooling water, nevertheless by design it is possible to ensure that the side and end walls are of substantially equal thickness.

In conventional engines the walls of the crankcase are locally thickened at their junctions with adjacent walls and along their free edges, and usually incorporate strengthening ribs. In such constructions the thickened portions constitute the equivalent of a frame interconnected by thinner panels. In such an engine the thickened portions constituting the frame carry the majority of the stress imposed on the crankcase when the engine is operative and the relatively thin portions which are equivalent to panels magnify the vibration imparted to the frame,

since the middle of each panel will vibrate at an amplitude considerably greater than the relatively rigid frame portion.

' By a construction in accordance with this invention there is no equivalent to a frame and interconnecting panels since the thickness of the crankcase wall is approximately uniform even at the junctions between adjacent walls. In the case of a single wall, the variation in thickness along any one wall should not be greater than 13:1 and the variation in thickness between any two walls should be not more than 1.5: 1. It will be appreciated that where an external wall is joined to an internal wall, the external wall must possessgreat rigidity and inasmuch as the vibrations are imparted to the external wall by the internal wall, this portion of the external wall must be regarded as the periphery of the wall. Moreover, since the Amplitude of vibration at the middle of the wall Amplitude of vibration of the periphery of the wall To calculate the required wall thickness, it is only necessary to determine the required thickness of the wall at the point of greatest stress and make .all Walls of the same thickness. The dynamic magnification factor when applied to panels of the type under consideration has reference to a ratio of the amplitude of vibration at the middle of the panel or wall as compared with the amplitude of vibration at the periphery of the wall. The periphery of the wall is subjected to the vibrations developed by the reciprocating components of the engine and a relatively small amplitude of vibration at the periphery of a panel or wall results in a much larger amplitude of vibration at the middle of the Wall. Hence, the dynamic magnification factor is a ratio of the two amplitudes and has not units.

Since the thickness of the major portion of the crankcase wall will, by the present invention, be thicker than is normal, it is convenient to construct the crankcase from a relatively light material such, for example, as aluminium or magnesium.

The crankcase/cylinder block casting of either a conventional engine or an engine of the kind described, before being built-up, is substantially undamped, so that any part may have a dynamic magnification factor of 20 or more. When built-up into a complete engine, however, the main structure of either type of construction becomes heavily damped i.e. it may have a dynamic magnification factor of less than 3. In a conventional engine this applies only to a very limited extent to the relatively thin panels connecting the load-carrying thick portions so that the panels may have a dynamic magnification factor as great as 10, in the structure specified the whole structure is similarly damped including the side walls so that their dynamic magnification factor is less than 3. Thus, if the vibration levels of the load-carrying part of the structure are comparable in the two engines, the levels in the centre regions of the side walls are reduced relatively in the engine of the specified structure by some 10 db and the noise emitted is also reduced by some 10 db.

Since materials such as aluminium or magnesium alloys will, for a given strength in tension, be thicker than cast iron they will be more rigid in bending and the natural frequency of any portion of the surface in a given mode will be increased. This tends to displace the natural frequencies of portions of the engine surface to higher frequencies (i.e. above the 1000 to 3000 c./s. region) at which the human ear is less sensitive.

It has been found from experiment that in order to achieve a worthwhile reduction in noise emitted by the engine the dynamic magnification factor of each wall should not exceed 3.

The invention is not to be confined to any strict conformity to the showings in the drawings but changes or modifications may be made therein so long as such changes or modifications mark no material departure from the spirit and scope of the appended claims.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A frameless crankcase for an engine including interconnected end .and side walls constituting the outer surface of the crankcase and said walls having a dynamic magnification factor of not more than 3.

References Cited UNITED STATES PATENTS 1,286,621 12/1918 Herreshoff 92147 1,287,386 12/1918 Mas-ury 92-147 FOREIGN PATENTS 249,974 4/ 1926 Great Britain.

OTHER REFERENCES S.A.E. Journal, January 1965, vol. 73, No. 1, p. 60. The High Speed Internal Combustion Engine Third Edition, by Ricardo and Glyde Interscience Publishers, Inc., New York, NY, reprinted 1944, pp. 178 and 179, 180 and 181.

WENDELL E. BURNS, Primary Examiner. 

